2. Description of the Prior Art
It is common practice in the conveyor art to provide scrapers for conveyor belts. Generally these scrapers are provided on the underside of the belt to scrape debris from the belt surface just after the belt starts its return flight after rounding a head pulley. An apparatus typical of that design is disclosed in U.S. Pat. No. 3,598,231.That patent further discloses the common practice of staggering or offsetting the scraping blades along the width of the belt in an attempt to prevent debris from jamming and/or freezing between adjacent scraping blades. Typically, these offset blades are made of metal or at least contain a sharpened metal edge. That design allows for ready adjustment of individual blades but causes significant problems under high load pressure.
Other prior art designs utilize scraping blades arranged at an angle to the belt which plow or hoe debris off to one side. That type of arrangement is disclosed in U.S. Pat. No. 3,504,786. Plowing arrangements, as well as staggered arrangements, attempt to remove debris quickly, thus effecting better cleaning while eliminating buildup and/or freezing between adjacent scraping blades. Both of those arrangements typically scrape debris from the belt at approximately a 90.degree. angle in relation to the belt surface. With the 90.degree. design the blades must be staggered, because, if all blades were positioned next to one another, debris would bunch up quickly and render the scraping apparatus inoperative and/or ineffective.
Staggered blade arrangements are not without their own problems, however. With a staggered blade arrangement, an unequal tension may be imparted to the belt surface and, effectively, there could be more tension on one blade than on another. Also with that arrangement, one may be forced to change blades under dangerous field conditions by requiring a workman to crawl or reach into a conveyor chute while using tools to change the blades. This is illustrated in U.S. Pat. No. 4,249,650, where nuts have to be loosened and tightened every time a blade has to be changed or adjusted.
A further problem with staggering and/or plowing, and particularly with metal blades, is that under high load pressure the blades may twist or turn sideways, thereby bending the support arm, loosening the bolt attaching the arm and blade, misaligning the belt, and/or tearing the belt surface. Blade twisting or turning which causes belt tearing can destroy thousands of feet of belt, which can be quite costly to replace.
In the past, scraping blades have only been between about 1/8 inch to 1/2 inch thick. For example, U.S. Pat. No. 4,533,036 discloses a plurality of thin scraping blades mounted on single or multi-armed resilient supports. That patent shows the blades to be arranged side-by-side, with the intermediate blades supported by only a single arm. However, such an arrangement does not suggest that the individual thin blades can be positioned in side-by-side abutting relation to prevent blade twisting by providing mutual lateral support and pivotal stability. In fact, that patent discloses outer blades mounted on two supporting arms to achieve greater structural rigidity. That patent further discloses supporting arms containing resilient couplings for providing shock absorbency at the expense of possible blade twisting or turning. Although that patent discloses shaving of the belt surface, as opposed to plowing, it does not address the problem of blade twisting nor does it provide a solution for eliminating its occurrence.
The tensioning of most prior art belt scrapers against the belt surface has been accomplished by an external tensioning system. Examples include counterweight designs, ratchet tensioners, air cylinders, torsion arms and air bags. Although effective, these systems are cumbersome and require a lot of space for installation and maintenance. Additionally, dangerous conditions may result if the scraping apparatus gets caught by the belt while a person is making adjustments or standing nearby. This condition could cause a lever arm or counterweight to rotate or move unexpectedly, causing bodily harm. Since the arm of the scraper is often secured to a rotatable transverse support shaft either through a spring or elastomeric biasing mechanism, each arm and blade is also made rotatable. Therefore, if the conveyor belt were to suddenly reverse its direction of movement, (i.e. due to an inclined conveyor or a malfunctioning pulley brake) belt pressure could cause the blades and support arms to rotate or be torqued backwards thus breaking or bending the entire scraping apparatus. The blades could end up at various angles to the belt surface. Thus, once the belt is restarted and made to travel in its intended direction, the damaged arms and blades could flip back to their original positions thereby cutting or tearing the belt surface.
The novel apparatus of the present invention overcomes the foregoing deficiencies of prior art scrapers by providing an apparatus which shaves the surface of conveyor belts in angled engagement to remove debris that has built up on the belt surface. The present invention accomplishes this result in a manner which minimizes damage to the belt surface and danger to those standing nearby. Accordingly, it is an object of the present invention to provide an apparatus for scraping conveyor belts which does not have the inherent deficiencies of the prior art.
Other objects and advantages of the present invention will become apparent to those skilled in the art with reference to the attached drawings and the description of the invention which hereinafter follows.